Seeking to save Europe's endangered written heritage
Iron gall ink is arguably the most important ink in Western history. Known since the Roman times, it became widely used after the late Middle Ages. But whilst its scriptural or pictorial quality is undisputed, the corrosive properties of its components threaten iron gall ink inscribed artworks and historically important writings. Due to the alarming data concerning deterioration caused by the corrosive ink, curators and art historians, as well as chemists and physicists joined forces within the EC funded INKCOR project. While art historians surveyed historical ink recipes, the physicists and chemists analysed the ingredients using high-tech methods. Historical recipes used in the preparation of gall ink varied, but they all share common colour forming ingredients, gallic acid from tannins and iron ions. The two main sources of ink corrosion of paper and parchment were identified to be acid hydrolysis and oxidation catalysed by ferrous ions. In addition numerous other transition metals, which can be present in historical iron gall inks, were found to catalyse similar degradation pathways. Chemists at the University of Ljubljana in Slovenia evaluated the anti- and pro-oxidative properties of gallic acid in the presence of Fe(III). Although a hydroxyl radical scavenger, gallic acid may exhibit pro-oxidative properties as it promotes the production of hydroxyl radicals due to iron chelation. The results of experiments pointed to an overall anti-oxidative effect where there is an excess of reactive iron ions present. On the basis of this knowledge, the INKCOR consortium started developing a non-aqueous conservation method for endangered documents. The stabilisation of iron gall ink containing paper will be achieved by the combined action of alkalies to combat acid hydrolysis and antioxidants to prevent oxidation.
